The present invention is especially designed to provide and improve the read/write head actuator assembly which is especially useful in small form factor disc drive systems. In a disc drive, the read/write heads are attached to an actuator arm, and extend from a pivot bearing assembly out over the disc where the information is stored. A voice coil magnetic motor extending in the opposite direction of the actuator arms from the actuator arms' pivot bearing provides the actuating force to move the arms about the pivot and position the heads over a desired portion or track on the disc. This arrangement is known as a head disc assembly.
The information supplied to the heads (write) or supplied by the heads (read) is normally carried by small wires from the heads to a point near the actuator arm pivot. A flexible printed circuit cable (PCC) is secured to the actuator arm near the pivot point, and the small signal carrying wires are soldered to exposed regions on the PCC. Additionally, the PCC has signal wires which carry signals to activate the moving coil motor, and thereby effectuate actuator arm rotation. Typically, the control signals for the motor and the read and write data from the heads carried by the pivot arm are carried over the PCC to a fixed circuit board located within the head disc assembly of the disc drive; this board typically includes a preamplifier to amplify the signals before sending them to a signal processing circuit elsewhere in the disc drive, or located on the outer surface of the disc drive housing.
In many previous disc drive designs, the flexible PCC was bent to form an arc between the circuit board and the arm, so that the PCC cable could move easily with the actuator arm without providing any significant biasing force against the arm. The one end of the PCC was then attached to the actuator arm and secured via an adhesive. The use of adhesive within the disc housing is usually to be avoided, except in an arrangement where no other choice is available, because adhesives may outgas and produce particles which will contaminate the discs and/or the heads. Additionally, the use of adhesives in manufacturing makes repeatable assembly very difficult and requires a cleaning step to minimize the amount of adhesive that is introduced into the disc drive environment. However, disc drive designers wishing to avoid adding mass to the actuator arm have frequently deemed a small amount of adhesive necessary, at the expense of outgassing problems and repeatability.
Recognizing the side effects of using adhesives in disc drives, other means for attaching the PCC to the actuator arm have developed, frequently utilizing a screw-in clamp structure as shown in the prior art of FIG. 1A of the present application. According to this approach, the actuator arm attachment end 2 of the PCC cable 4, includes a small hole 8 which is aligned with the hole 5 in an attachment bracket 6. A special washer 7 and screw 9 are provided, the screw 9 passing through a washer 7, hole 8 in the PCC 4, the hole 5 in the attachment bracket 6, and into a hole 10 in a mounting boss 12 on the side of the actuator arm 14. However, in order to utilize this approach, the assembler of the disc drive whose task was to attach the PCC to the actuator arm had to hold three pieces in one hand, that is, attachment bracket 6, the PCC 4, and the specially formed washer 7, and maintain these in an aligned position as he/she threaded the screw 9 through the three holes 8, 5 and 10, and into the mounting boss 12 on the side of the actuator arm 14.
It was further very important in addition to maintaining alignment, to keep all of these individual parts from turning while the screw is torqued into the final, hold down position. Maintaining alignment between the PCC 4 and actuator arm 14 is especially important. When utilizing the screw and bracket combination of the prior art as exemplified in FIG. 1, special care had to be exercised to prevent the PCC from rotating. As the screw is tightened, rotation would often result. As long as this remained a possibility, a larger keep-out area for the PCC within the disc drive envelope always had to be maintained; lacking such a step, a separate alignment apparatus or process had to be utilized, at a considerable added expense.
Another significant issue in motor cable attachment design is that motor sizing for the voice coil motor utilized to position the actuator arm must take into account both the bias against the arm due to the arc in the PCC, and the weight of any components incorporated in the PCC. Bias is the resultant force on the actuator arm which is due to the arc in the PCC. Because of the positioning of the preamplifier circuit 121 (FIG. 1B) within the disc drive envelope or housing 16, and the need to minimize the space occupied by the total disc drive housing, some cable curvature with a resultant arc is inevitable. The bias created by the PCC arc can cause pivoting of the arm to an arbitrary position. The bias must be overcome by the actuator motor to reposition the arm.
A PCC cable which is put in a severely crimped position creates a large bias, and requires a more powerful voice coil motor to overcome the bias. In smaller form factor disc drives, it is desired to design the actuator motor as small as possible. This requires using low mass parts, reducing bearing friction and minimizing the bias created by the PCC against the actuator arm. Necessarily, the greater the stiffness and weight of the PCC and its connecting elements, the larger the resulting bias. Thus, it is important in designing the attachment to have the attachment elements cooperate with the cable in such a way to make sure that the bias is consistent over the entire operating range of the voice coil motor and the actuator arm so that the actuator motor is designed and operated to overcome a specific known bias; and the attachment element must have minimal weight so that the actuator motor size does not have to be enlarged just to overcome the PCC bias against the arm.